The present invention generally relates to flat inductors. More specifically, the present invention relates to flat inductors for induction heating, melting, or holding metal at temperature.
Flat inductors are generally known and used in induction applications. They are used primarily in induction heating applications. In order to achieve a reasonable electrical efficiency using flat inductors, it is essential to keep the distance between the flat inductor coil and the load small and relatively constant.
In melting applications, the induction coil must typically be separated from the liquid metal by refractory materials, necessarily increasing the distance between the melt and the coil and thereby decreasing efficiency. This low efficiency has prevented the use of flat inductors for melting applications.
In addition, in induction heating and melting, one wishes to avoid heating metal parts adjacent to a workpiece or charge. This requires guiding the magnetic flux produced by the induction coil from the backside and circumference of an-induction coil with shunts. This is conventionally achieved using shunts made from laminated steel. Due to the complexity of the shunts, they are difficult and expensive to make.
Because of these perceived drawbacks, induction heating and melting are not considered viable in some industries. Typically, the aluminum industry, for example, melts and holds metal at high temperatures using gas burners. Large holding furnaces are used, typically in the range of 100,000 to 200,000 pounds of capacity. The use of gas burners presents several disadvantages. When burners above the voluminous metal bath are used, the metal is held at temperature through radiation due to temperature differences between the flame and the metal in the upper section of the furnace. Thermal energy is usually transferred throughout the metal bath through a layer of dross. Therefore, the further the metal resides from the burner the more difficult it is to heat and hold the metal at temperature. Every gas burner requires an exhaust and the thermal efficiency is limited to the burner itself. Because the burners transfer heat only through radiation, they do not produce a stirring action. The industry has tried mechanical stirrers as well as electromagnetic stirrers. While mechanical stirrers are not expensive to produce and install, they require significant maintenance, thereby increasing operational costs. Electromagnetic stirrers have been applied either under the furnace, or on the side, but they are quite expensive to operate.
Other drawbacks of gas burners include significant air pollution, temperature control, and high refractory costs due to exposure to high temperatures.
The present invention makes it possible to heat and stir metals by induction, which eliminates the drawbacks of gas burners.
The present invention provides a flat inductor heating system comprising a flat induction coil and a housing for the inductor coil. The housing comprises a thermal insulating layer abutting the induction coil and an enclosure engaging the insulating layer to enclose the induction coil. An aggregate material comprising a mixture of shot and a binding material reside in the housing, consuming all space within the housing about the induction coil.
The flat inductor heating system may also include a support for suspending the housing and aggregate material above a vessel that holds a metal to be inductively heated, melted and/or stirred by the flat inductor system. A drive mechanism cooperating with the support moves the housing either toward or away from the vessel. A sensor may be provided for sensing the distance between the housing and the surface of the metal in the vessel. The sensor may be coupled to a controller for actuating the drive mechanism in response to a signal from the sensor.
Three induction coils maybe arranged in the housing and connected to a three-phase supply having each phase 120 electrical degrees out of phase with respect to the other two phases. Each of the three phases is connected to one of the three induction coils.